Effect of Aeration on Organic Acid Production by Propionibacterium shermanii

Propionibacteria have been reported as being oxygen sensitive bacteria. Nevertheless, in this work, we intend to show that Propionibacterium shermanii CDB 10014 is able to grow even at high volumetric oxygen transfer coefficients (KLa). Similar final cell concentrations were achieved in experiments at different KLa values, with increasing cell yield from 0.08 g/g cells in anaerobic con­ ditions to 0.22 g/g at KLa 61 h~ . The organic acid pro­ duction pattern changes depending on the KLa. At KLa higher than 36 h -1, propionic acid was not produced and acetic acid was the main product. At KLa higher than 20 h_1, lactic acid began to be produced. In further studies, no important differences in the growth yield were ob­ served in the pH range 5.5-7.0, while the cell production was enhanced by temperatures in the range 30-35 °C.